The Penal Laws were, according to Edmund Burke "a machine of wise and elaborate contrivance, as well fitted for the oppression, impoverishment and degradation of a people, and the debasement in them of human nature itself, as ever proceeded from the perverted ingenuity of man."[3]

Initially, the dual monarchs of England and Ireland were cautious about applying the Penal Laws to Ireland because they needed the support of the Catholic upper classes to put down the Gaelic Irish rebellion in the Nine Years War (1594–1603). In addition, a significant section of the Catholic aristocracy was Old English who had traditionally been loyal to English rule in Ireland. However, the ascent of James VI of Scotland to both the English and Irish thrones as James I in 1603 and the eventual victory in the Nine Years War saw a series of coercive new laws put into force. In 1605 the 'Gunpowder Plot' was planned by a group of English Catholics, who were disappointed in their hopes that James would relieve laws against Catholics. This provided a further impetus and justification for restrictive laws on Catholics in Ireland, Scotland and England. In 1607 the Flight of the Earls seeking Catholic help in Europe for a further revolt set the scene for a wholesale Plantation of Ulster by the Scots and English.

From 1607, Catholics were barred from holding public office or serving in the army. This meant that the Irish Privy Council and the Lords Justice who, along with the Lord Deputy of Ireland, constituted the government of the country, would in future be Anglicans. In 1613, the constituencies of the Irish House of Commons were altered to give plantation settlers a majority. In addition, Catholics in all three Kingdoms had to pay 'recusant fines' for non-attendance at Anglican services. Catholic churches were transferred to the Anglican Church of Ireland. Catholic services, however, were generally tacitly tolerated as long as they were conducted in private. Catholic priests were also tolerated, but bishops were forced to operate clandestinely. In 1634 the issue of the "Graces" arose; generous taxation for Charles I (whose Queen Henrietta Maria was Catholic) was voted by Irish Catholic landlords on the understanding the laws would be reformed, but once the tax was voted Charles' viceroy refused two of the 51 Graces, and subsequent bills were blocked by the Catholic majority in the Irish House of Lords.

Catholic resentment was a factor in starting the Irish Rebellion of 1641 and the establishment of Confederate Ireland from 1642 with Papal support, that was eventually put down in the Cromwellian conquest of Ireland in 1649–53. After the Act of Settlement in 1652, Catholics were barred from membership in the Irish Parliament, and the major landholders had most of their lands confiscated under the Adventurers Act. They were banned from living in towns for a short period. Catholic clergy were expelled from the country and were liable to instant execution when found. Many recusants had to worship in secret at gathering places (such as Mass rocks) in the countryside. Seventeen Catholic martyrs from this period were beatified in 1992.

The Roman Catholics of this kingdom shall enjoy such privileges in the exercise of their religion as are consistent with the laws of Ireland, or as they did enjoy in the reign of king Charles the second: and their majesties, as soon as their affairs will permit them to summon a parliament in this kingdom, will endeavour to procure the said Roman Catholics such farther security in that particular, as may preserve them from any disturbance upon the account of their said religion.

The quid pro quo to attain these privileges involved swearing an oath of loyalty to William and Mary. Many Catholics found this oath repugnant when the Papacy started to support the Jacobites in 1693. A small number of Catholic landlords had sworn this loyalty oath in 1691–3 and their families remained protected. Previous Jacobite garrison surrenders, particularly the agreement at Galway earlier in 1691, specifically provided that the Catholic gentry of counties Galway and Mayo were protected from the property restrictions, though they would be excluded from direct involvement in politics.

Articles 2 and 9 required that:

2. .... provided also, that no person whatsoever shall have or enjoy the benefit of this article, that shall neglect or refuse to take the oath of allegiance, made by act of parliament in England, in the first year of the reign of their present majesties, when thereunto required.

9. The oath to be administered to such Roman Catholics as submit to their majesties' government, shall be the oath abovesaid and no other.

At the European level, this war was a part of the War of the Grand Alliance, in which the Holy See supported William III's alliance against France, and on the news of the Battle of the Boyne a Te Deum was sung in thanksgiving at the Vatican. But from 1693 the Papacy changed its policy and supported James against William, and William's policy also moved from a degree of toleration for Catholics to greater hostility. By then, King James was based in France at Saint Germain, and was supported politically and financially by Louis XIV, the long-standing enemy of William and Mary. Religion eventually became an issue in defining a notable family's loyalty to the crown.

With the defeat of Catholic attempts to regain power and lands in Ireland, a ruling class which became known later as the "Protestant Ascendancy" sought to ensure dominance with the passing of a number of laws to restrict the religious, political and economic activities of Catholics and Dissenters. Harsher laws were introduced for political reasons during the long War of the Spanish Succession that ended in 1714. The son of James II, the "Old Pretender", was recognised by the Holy See as the legitimate king of Britain and Ireland until his death in 1766, and Catholics were obliged to support him. He also approved the appointments of all the Irish Catholic hierarchy, who were drawn from his most fervent supporters. These aspects provided the political basis for the new laws passed for several decades after 1695. Interdicts faced by Catholics and Dissenters under the Penal Laws were:

Exclusion of Catholics from most public offices (since 1607), Presbyterians were also barred from public office from 1707.

Ban on intermarriage with Protestants; repealed 1778

Presbyterian marriages were not legally recognised by the state

Catholics barred from holding firearms or serving in the armed forces (rescinded by Militia Act of 1793)

On a death by a Catholic, his legatee could benefit by conversion to the Church of Ireland;

Popery Act – Catholic inheritances of land were to be equally subdivided between all an owner's sons with the exception that if the eldest son and heir converted to Protestantism that he would become the one and only tenant of estate and portions for other children not to exceed one third of the estate. This "Gavelkind" system had previously been abolished by 1600.

Ban on converting from Protestantism to Roman Catholicism on pain of Praemunire: forfeiting all property estates and legacy to the monarch of the time and remaining in prison at the monarch's pleasure. In addition, forfeiting the monarch's protection. No injury however atrocious could have any action brought against it or any reparation for such.

Ban on Catholics buying land under a lease of more than 31 years; repealed 1778.

Ban on custody of orphans being granted to Catholics on pain of 500 pounds that was to be donated to the Blue Coat hospital in Dublin.

Ban on Catholics inheriting Protestant land

Prohibition on Catholics owning a horse valued at over £5 (to keep horses suitable for military activity out of the majority's hands)

Roman Catholic lay priests had to register to preach under the Registration Act 1704, but seminary priests and Bishops were not able to do so until 1778

When allowed, new Catholic churches were to be built from wood, not stone, and away from main roads.

'No person of the popish religion shall publicly or in private houses teach school, or instruct youth in learning within this realm' upon pain of twenty pounds fine and three months in prison for every such offence. Repealed in 1782.[5]

Any and all rewards not paid by the crown for alerting authorities of offences to be levied upon the Catholic populace within parish and county.

Historians disagree on how rigorously these laws were enforced. The consensus view is that enforcement depended on the attitudes of local magistrates bringing or hearing particular cases; some of whom were rigorous, others more liberal.

From 1758, before the death of James III, ad-hoc groups of the remaining Catholic nobility and merchants worked towards repeal of the penal laws and an accommodation within the Hanoverian system. These were based locally on county lines. An earlier attempt in 1727 had met with strong opposition from the Jacobite movement, which resisted any negotiations with the Hanoverians, being usurpers.[6] By 1760 eminent Catholics such as Lord Trimlestown, Lord Kenmare and Charles O'Conor of Belanagare persuaded the more liberal Protestants that they presented no political threat, and that reforms must follow. Events abroad in the 1760s, such as the outcome of the Seven Years war, the death of the Old Pretender (1766), the emerging "Age of Enlightenment", and the Suppression of the Society of Jesus by Europe's Catholic monarchs, all seemed to confirm their position.

On the death of the "Old Pretender" in January 1766 the Holy See recognised the Hanoverian dynasty as legitimate, and so the main political basis for the laws was removed and the slow process of Catholic Emancipation began, with the repeal of some of the Penal Laws by the Catholic Relief Acts of 1771, 1778 and 1793.[7] However, the long drawn-out pace of reform ensured that the question of religious discrimination dominated Irish life and was a constant source of division. In a show of goodwill, John Carpenter, titular Archbishop of Dublin, technically still an illegal position, was invited to join the Royal Dublin Society in 1773.[8]

An Irish Act of 1774 allowed any subject of George III "of whatever persuasion to testify their allegiance to him".[9] The Quebec Act of 1774 was an encouragement outside Ireland, with the London parliament restoring religious rights in the main part of Canada, followed in Britain and Ireland by the Catholic Relief Act 1778. Carlow College was established in 1782.

Opposition to Catholic Relief ensured that when relief was granted it was often accompanied by what were seen to be unpleasant concessions to the system. Relief in 1793 was accompanied by a widely unpopular Militia Act which removed the ban on Catholics holding firearms to allow for their conscription into the militia, but not their admittance into the officer ranks. However, wealthier Catholics did not oppose this as it was further proof of their gradual inclusion into the establishment.

France declared war on Britain and Ireland in February 1793 and the war took priority over further reliefs. The French government opposed the Holy See from 1790. Irish Catholic priests were trained in France, Belgium, and Spain. Prime Minister Pitt proposed to fund the establishment of St. Patrick's seminary in Maynooth in 1795. The French republican policies of "Dechristianization" in 1790–1801 were often similar to Cromwell's anti-Catholic policies in Ireland in the 1650s. The Presbyterian Church was granted the Regium Donum In 1795 the new viceroy the earl of Fitzwilliam proposed full political emancipation as suggested by Grattan, and a prelude to proposals for Parliamentary union. He was removed within weeks by the hardliners in the Irish administration.

Many reformers despaired of peaceful change, particularly in the lack of Tithe reform, and this led on to instances of Catholic involvement in the abortive 1798 rebellion. During the rebellion the Irish Catholic bishops supported the government line. The subsequent passing of the Act of Union of 1801 was intended to include Catholic Emancipation, as power was moved from the hands of the Protestant Ascendancy to the London Parliament. This was agreed by most of the British Cabinet, including William Pitt, and they resigned when it was not effected. The personal opposition of George III ensured that no change would be forthcoming during his reign.

The political argument for emancipation to allow Catholic MPs to sit in parliament continued after the 1801 Act of Union, supported by liberal MPs such as Henry Grattan. Division arose over the "veto", the issue whether the government could, or could not, veto the appointment of a bishop where he was approved by the Pope. In May 1823, Daniel O'Connell launched the Catholic Association and campaigned for Catholic emancipation which was largely achieved in 1829, primarily benefitting the middle classes. While this was seen as a late and overdue reform by Irish Catholics, Irish Dissenters had only just achieved the same status following the 1828 Test Act, Irish Jewish MPs were barred until 1858 and atheists until 1886.

The Act also allowed for Catholic judges and senior civil servants and state officials to be appointed. As with the election of MPs, those who benefitted were the better educated and richer Catholics. The same class took advantage of the reform of town and city corporations in the Act of 1840 and took part in local government. But for the majority of Irish Catholics living in the countryside, the cost of the tithing system had always been the main cause of complaint.

The obligation by Catholics and other religious groups to pay tithes to the Protestant Church remained until its disestablishment by the Irish Church Act 1869 and Catholic Emancipation was quickly followed by a period of violent resistance known as the Tithe War. From 1840 tithes were no longer payable by tenants but by their landlords, who were allowed to increase rents to make up the difference. The Catholic Church became resurgent from the 1840s, uniting with the Protestant churches to oppose the integration of students of differing religion in the new primary or 'National' schools, and in the 1850s a debate arose over whether some proposed universities should be mixed or just for Catholics.

Section 5(2) of the Government of Ireland Act 1920 repealed in Ireland 'any existing enactment by which any penalty, disadvantage, or disability is imposed on account of religious belief or on a member of any religious order'.

As a result, in tandem with Section 37(1), Roman Catholics once again became eligible to occupy the office of Lord Lieutenant of Ireland, the British monarch's representative in Ireland. Within months of this legislation passing, Viscount FitzAlan of Derwent became in April 1921 the first Roman Catholic Lord Lieutenant of Ireland since the penal laws forbade such appointments in 1685. Because of the establishment of the Irish Free State in 1922 and the altered constitutional relationship between Ireland and the United Kingdom, FitzAlan was also the last Lord Lieutenant of Ireland.

The memory of the Penal laws remained as a strongly resonant cultural element in Irish Catholicism long after their reform, and they were seen as a social and legal nadir from which the bulk of the Irish population had eventually escaped.

The position of Irish Catholics is a cruel one. We are enslaved by a Protestant power. The penal laws against our religion are not yet abolished in full. The injurious social and economic results of these anti-Catholic laws will not be overcome for generations. To the present day we suffer political injury inside and outside of Ireland, simply and solely because we are practising Catholics. Sons of martyrs, we are known in every Masonic lodge and every anti-Catholic country as 'Papists', and par-excellence, the most devoted of all the children of the Holy See.[10]

In 1971, responding to news of an importation of contraceptive devices from Northern Ireland that could not be sold in the Republic, Thomas Ryan, Bishop of Clonfert, said that "... never before, and certainly not since penal times was the Catholic heritage of Ireland subjected to so many insidious onslaughts on the pretext of conscience, civil rights and women's liberation."[11]